A conventional lateral flow test apparatus comprises an elongate membrane along which a sample analyte flows. The sample analyte may or may not contain a test molecule at a concentration level of interest. Typically, at a specific test region, the membrane is impregnated with molecules which are chosen because they interact either with the test molecule, or with a marker molecule which may be conjugated with the test molecule. The impregnated molecules are typically bioreceptors. The presence of the test molecule in the sample analyte, at or above the concentration level of interest, results in an accumulation of the markup at the test line. Provided the marker is optically active, once a sufficiently high concentration of markers has accumulated at the test line, this may be observed by the user of the test apparatus. The test region is typically defined as a test line which extends across the membrane, but does not extend significantly along it, so may have dimensions of: the membrane width (across the membrane)×0.5-1.5 mm and typically 1 mm (along the membrane).
In order to avoid false-negative results (or in some instances false positive, as will be discussed below in relation to competitive assays results), lateral flow tests generally include a control line at which marker molecules may also accumulate. The presence of a visual change at the control line provides confirmation of adequate flow along the lateral flow test apparatus.
In order to reduce the inherent subjectivity of a visual inspection by the user, it has been proposed to replace the visual inspection by an integrated optical system. Such an optical lateral flow test system which uses LEDs as a light source and photodiodes as an optical measuring device is disclosed in international patent application Publication WO2009/144507-A1.
International patent application Publication WO02/10754 discloses an assay apparatus comprising a means of providing quantitative measurement of an analyte in which a meter determines, with polymer coated electrodes, the increase in capacitance of a region of a test strip, wherein the change in capacitance is directly related to the quantity of bound labelled target analyte, and thus to the quantity of target analyte in a patient sample.